Catalysts for fluoroolefins hydrogenation

ABSTRACT

A support of metal oxyfluoride or metal halide for a metal-based hydrogenation catalyst useful in hydrogenating fluoroolefins is provided.

BACKGROUND

1. Field of Invention

The present invention relates to catalysts for hydrogenating olefins.More particularly, this invention relates to supported catalyst forhydrogenating fluoroolefins.

2. Description of Prior Art

Catalytic hydrogenation of fluoroolefins is frequently used in producinghydrofluorocarbons as useful products and/or intermediates. Variousmetals, such as Pd, supported on a substrate have long been recognizedas highly effective hydrogenation catalysts. These catalysts areparticularly effective in gas-phase reactions.

In certain reactions, the effectiveness of these catalysts can beincreased by incorporating at least one zero-valent metal onto asupporting substrate. Materials such as alumina, silica, titania, andzirconia, as well as titanium oxide, magnesium oxide, and zirconiumoxide are known substrates for certain hydrogenation catalysts. (U.S.Pat. No. 5,089,454). Knunyants et al. (see Izv. Akad. Nauk. SSSR, (1960)1412-1418) reports a Pd/Al₂O₃ catalyst used to catalyze thehydrogenation of CF₃CF═CF₂ (HFP) to CF₃CHFCHF₂ (236ea), and CF₃CF═CHF(1225ye) to CF₃CHFCH₂F (245eb). However, due to the occurrence ofhydrogenolytic cleavage of the carbon-fluorin bond, small amount of HFis generated during reaction, which attacks alumina, silica, titania,and zirconia that are known as the normal carrier of palladium, causingcatalyst structure change and catalyst deactivation. Japan Patent JPPatent 3543863 teaches the use of a Pd/carbon catalyst that is resistantto HF attack for the hydrogenation of HFP to 236a. U.S. Pat. No.5,396,000 teaches the use of a Pd/carbon catalyst for the hydrogenationof 1225ye to 245eb. However, these carbon supported metal catalysts arenot regenerable once deactivated. Therefore, there is a need for a newtype of catalyst that is not only resistant to HF attack but alsoregenerable once deactivated for the hydrogenation of fluoroolefins.

SUMMARY OF THE INVENTION

Applicants unexpectedly found that metal catalysts supported on metaloxyfluorides and certain metal fluorides provide stable activity for thehydrogenation of fluoroolefins, while those supported on metal oxidesexhibit unstable activity.

Accordingly, in one aspect of the invention provided is an article ofmanufacture comprising (a) a solid support comprising a metaloxyfluoride or a metal fluoride, wherein said metal fluoride is selectedfrom the group consisting of CrF₃, TiF₄, and ZrF₄; and (b) at least oneelemental metal disposed on or within said support, preferably whereinsaid elemental metal is present in an amount from about 0.05 to about 10weight percent based upon the total weight of the metal and support. Incertain preferred embodiments, the carrier of the catalyst is selectedfrom the group consisting of oxyfluorides of Al, Cr, Ti, Zr, Mg, etc.,or metal fluorides selected from the group consisting of CrF₃, TiF₄, andZrF₄. Non-limiting examples of elemental metals include Pd, Ru, Pt, Rh,Ir, Fe, Co, Ni, Cu, Ag, Re, Os, Au, and any combinations thereof.

According to another aspect of the invention, provided is a method forpreparing a catalyst comprising (a) contacting at least one metal salt,at least one solvent, and a metal fluoride or metal oxyfluoride to forma slurry; (b) removing said solvent from said slurry to form asolvent-free powder; (c) optionally calcining said powder; (d)transforming said powder into a supported catalyst; and (e) contactingsaid support catalyst with a gaseous composition comprising H₂ toactivate said supported catalyst, wherein said activated supportedcatalyst comprises about 90 to about 99.95 weight percent of metalfluoride or metal oxyfluoride and about 0.05 to about 10 weight percentof a zero-valent metal derived from said metal salt. In a preferredembodiment, the method comprising the steps of (a) dissolving a salt ofmetal component (e.g., Pd(NO₃)₂, PdCl₂ for Pd) in a suitable solvent toform a solution; (b) adding a suitable amount of metal oxyfluoride ormetal fluoride into said solution to form a slurry; (c) driving off thesolvent from said slurry to form a paste; (d) drying said paste to formsolvent-free powder; (e) calcining said solvent-free powder in N₂ flowfor 2 to 8 hours at 300-500° C.; (f) grinding the calcined powder to afinely divided state; (g) palletizing said fine powder into tablets; and(h) reducing said catalyst pellets in H₂ or diluted H₂ flow for 2 to 4hours at 150-250° C. prior to use.

According to yet another aspect of the invention, provided is a methodfor hydrogenating a compound comprising contacting a reactant comprisingan olefin having at least one carbon-fluorine bond with a supportedhydrogenation catalyst under reaction conditions effective to form areaction product comprising a hydrogenated derivative of said olefin,wherein said supported hydrogenation catalyst comprises (a) an elementalmetal selected from Pd, Ru, Pt, Rh, Ir, Fe, Co, Ni, Cu, Ag, Re, Os, Au,and any combinations thereof; and (b) a support comprising at leastabout 75 wt. % of a metal fluoride selected from the group consisting ofCrF₃, TiF₄, and ZrF₄, or a metal oxyfluoride selected from the groupconsisting of magnesium (II) oxyfluoride, aluminum (III) oxyfluoride,chromium (III) oxyfluoride, titanium (IV) oxyfluoride, and zirconium(IV) oxyfluoride. A preferred embodiment of this method comprises thesteps of (a) adding hydrogen and a fluoroolefin to a reaction vesselcontaining a hydrogenation catalyst; and (b) reacting said fluoroolefinwith hydrogen over said hydrogenation catalyst to produce ahydrofluorocarbon. Non-limiting examples of hydrofluorocarbons that canbe produced through the hydrogenation of certain fluoroolefins include1,1,1,2,3,3-hexafluoropropane (236ea), 1,1,1,2,3-pentafluoropropane(245eb), 1,1,1,3,3-pentafluoropropane (245fa),1,1,1,3-tetrafluoropropane (254fa), and 1,1,1,2-tetrafluoropropane(254eb).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

According to a preferred embodiment of the invention, selected supportedmetal catalysts are employed in the hydrogenation of fluoroolefins tohydrofluorocarbons. Non-limiting examples of metal components includePd, Ru, Pt, Rh, Ir, Fe, Co, Ni, Cu, Ag, Re, Os, Au, etc. The metalloading can varied within a large range, e.g., from 0.05-10 wt %.However, for noble metals such as Ru, Ph, Pd, Pt, Ir, etc., the metalloading is preferably lower than 5 wt %, and more preferably lower than1 wt %. There are two classes of catalyst supports useful in the presentinvention: (i) metal oxyfluorides, and (ii) metal fluorides selectedfrom CrF₃, TiF₄, and ZrF₄.

In certain preferred embodiments, the catalyst support is theoxyfluorides of metals, preferably bi-, tri-, and tetra-valent metals,more preferably tri-, and tetra-valent metals, and most preferablytri-valent metals. Component metals include, but are not limited to,Mg²⁺, Al³⁺, Cr³⁺, Ti⁴⁺, and Zr⁴⁺. In one embodiment, metal oxyfluoridesare prepared through fluorinating corresponding metal oxides with HF fora long enough time at a temperature higher than the reaction temperatureof fluoroolefin hydrogenation. The fluorine content in metal oxyfluorideis hence mainly determined by the temperature adopted in fluorinationprocess. No further reaction takes place between such prepared metaloxyfluoride and HF during the catalytic hydrogenation of fluoroolefins.

In certain preferred embodiments, the catalyst supports are thefluorides of metals, preferably bi-, tri-, and tetra-valent metals, morepreferably tri- and tetra-valent metals, and most preferably tri-valentmetals. Component metals include Cr³⁺, Ti⁴⁺, and Zr⁴⁺. In oneembodiment, metal fluorides are prepared by reacting metal hydroxidewith hydrofluoric acid. Since the metal is fully fluorinated, noreaction between metal fluoride support and HF generated as by-productis expected during the hydrogenation of fluoroolefins.

In certain embodiments, the catalyst of the present invention isprepared by adding the salt of a metal catalyst component (e.g.,Pd(NO₃)₂ or PdCl₂ for Pd) to an amount of solvent sufficient tosubstantially dissolve or solubilize the metal salt. The preferredsolvent is one in which the metal salt is readily soluble. The choice ofsolvent may vary depending on the particular metal salts. Examples ofsolvents that can be used for the preparation of the catalystcompositions of the present invention include water, alcohols, ethers,and mixtures thereof. Useful alcohols include monohydric and polyhydricalcohols. Most preferred alcohols are those that are monohydric and have1 to 5 carbon atoms. A most preferred solvent is water.

A metal oxyfluoride (e.g., AlO_(x)F_(y)) or metal fluoride (e.g., AlF₃)is then added to the solution of said metal salt to form a slurry. Afterformation of the slurry, substantially all of the solvent is removed toform a solid mass of a mixture of said metal salt and said metaloxyfluoride (or metal fluoride). Although the solvent can be removed inone step, a preferred method is to drive off a portion of the solventfrom the slurry to form a paste and then followed by drying the paste toform the solid mass. Any conventional technique can be used to drive offthe solvent. Examples of such techniques include vigorous stirring atroom or elevated temperatures, evaporation, settling and decanting,centrifugation, and filtration. It is preferred to evaporate off adesired amount of solvent to form the paste. The paste is then dried byany suitable method to form a free-flowing, substantially solvent-freepowder. Preferred methods for drying include oven drying, mostpreferably at temperatures from about 110° C. to about 120° C., andspray drying. Being solvent free means that less than 1 wt. %,preferably about 0.5 wt % or less, more preferably about 0.1 wt % orless, and most preferably no solvent will remain with the powder aftersolvent removal/drying. Upon removal of solvent, the powder will takethe form of a solid mass (or powder) of a mixture of particles of saidmetal salt and said metal oxyfluoride (or metal fluoride).

Optionally, the solid mass of the mixture of said metal salt and saidmetal oxyfluoride (or metal fluoride) powder is then calcined.Calcination is preferably carried out at a temperature of about 100° C.to about 750° C., more preferably at a temperature of about 200° C. toabout 600° C., and most preferably at a temperature of about 300° C. toabout 500° C. Calcination may further optionally be carried out in thepresence of an inert gas, such as nitrogen or argon.

After calcination, the powder is optionally further grinded such that itbecomes more finely-divided. The powder is further optionally pelletizedin order to form pellets.

The catalyst pellets are then loaded into a reactor and prior to use arereduced in hydrogen or diluted hydrogen flow for 2-4 hours at atemperature of about 50 to about 500° C., more preferably at atemperature of about 100 to about 300° C., and most preferably at atemperature of about 150 to about 250° C.

It may also be advantageous to periodically regenerate the catalystafter prolonged use while in place in the reactor. Regeneration of thecatalyst may be accomplished by any means known in the art. One methodis by passing oxygen or oxygen diluted with nitrogen over the catalystat temperatures of about 200° C. to about 600° C. (preferably about 350°C. to about 450° C.) for about 0.5 hour to about 3 days followed byreduction treatment in hydrogen or diluted hydrogen flow for 2-4 hoursat a temperatures of about 50° C. to about 500° C. (preferably about100° C. to about 300° C.).

Although it is contemplated that the hydrogenation of fluoroolefins maybe conducted in batch operation, it is preferred that the hydrogenationreaction is carried out as a substantially continuous operation.Furthermore, while it is possible that the hydrogenation reaction mayinvolve in certain embodiments a liquid phase reaction, it iscontemplated that in preferred embodiments the hydrogenation reactioncomprises, and even more preferably consists of, at least two vaporphase reaction stages.

With respect to the number of reaction stages, applicants have foundsurprisingly and unexpectedly found that overall reaction conversion andselectivity can be achieved at relatively high levels by the use of atleast two reaction stages wherein the first stage of reaction isconducted under conditions effective to achieve a first, relatively lowrate of conversion to produce a first stage reaction effluent, and atleast a second stage of reaction which is fed by at least a portion ofsaid first stage effluent and which is conducted under conditionseffective to achieve a second rate of conversion higher than said firstrate. Preferably, reaction conditions are controlled in each of thefirst and second stages in order to achieve the desired conversion inaccordance with the present invention. As used herein, the term“reaction conditions” is intended to include the singular and meanscontrol of any one or more processing parameters which can be modifiedby the operator of the reaction to produce the conversion of the feedmaterial in accordance with the teachings contained herein. By way ofexample, but not by way of limitation, conversion of the feed materialmay be controlled or regulated by controlling or regulating any one ormore of the following: the temperature of the reaction, the flow rate ofthe reactants, the presence of diluent, the amount of catalyst presentin the reaction vessel, the shape and size of the reaction vessel, thepressure of the reaction, and any one combinations of these and otherprocess parameters which will be available and known to those skilled inthe art in view of the disclosure contained herein.

Applicants have found that in preferred embodiments the step ofcontrolling the conversion in the first stage of the hydrogenationreaction is achieved by judicious selection and control of the amount ofcatalyst present in the first stage of reaction relative to the feedrate of one or more of the reactants and/or by judicious selection andcontrol of the reaction temperature, and preferably by judiciousselection and control of both of these process parameters. The step ofjudiciously selecting the amount of catalyst to be used in the firststage of reaction includes the step of estimating the amount of catalysttheoretically needed to convert 100% of the feed material. Such anestimate can be obtained by any and all known methods for making such anestimate, which should be apparent to those skilled in the art in viewof the teachings contained herein. In addition, the step of judiciouslyselecting the amount of catalyst may also involve conducting bench,pilot or similar studies to determine the amount of the particularcatalyst being used which is needed to convert 100% of the feed materialunder the feed rate in other process parameters which have otherwisebeen chosen. Based upon this estimate, the preferred embodiments of thepresent invention then include the step of providing in the first stageof reaction an amount of catalyst that is substantially below the amountrequired for 100% conversion, and even more preferably is sufficientlylow so as to result in a conversion of the feed olefin of from about 10%to about 60%, more preferably from about 10% to about 40%, and even morepreferably from about 10% to 25%. Once again, those skilled in the artwill appreciate that the step of judiciously choosing the amount ofcatalyst may further include running additional bench, pilot or otherstudies with the reduced amount of catalyst and adjusting the amount ofcatalyst accordingly. It is contemplated that all such studies andestimates can be achieved without undue experimentation in view of theteachings contained herein.

Applicants have found that the step of maintaining a relatively lowconversion of reactant in accordance with the present invention in afirst stage of reaction has an advantageous affect on the selectivity ofthe reaction to the desired hydrofluorocarbon. In other words, althoughthe amount of conversion which occurs in the first stage of reaction iscontrolled to be well below that which is desired for the overallhydrogenation step, applicants have found that an improved, higherpercentage of the feed material is converted to the desiredhydrofluorocarbon in the first reaction stage (that is, improvedselectivity is achieved) by controlling the conversion as describedherein. More specifically, is preferred in many embodiments that theselectivity to the desired hydrofluorocarbon in the first reaction stageis at least about 80%, more preferably at least about 90%, and even morepreferably at least about 95%, and in many preferred embodiments about97% or greater.

In certain preferred embodiments the step of controlling the conversionin the first reaction stage further includes removing heat from thereaction by cooling at least a portion of the reaction mixture. It iscontemplated that those skilled in the art will be able to devisewithout undue experimentation and many means and mechanisms forattaining such cooling in view of the teachings contained herein and allsuch means and mechanisms are with the scope of the present invention.

In preferred embodiments, at least a portion of the effluent from thefirst reaction stage is fed directly, or optionally after some furtherprocessing, to a second reaction stage in which the unreactedfluoroolefin remaining in the effluent after the first reaction stage isconverted to the hydrofluorocarbon in accordance with the presentinvention. More specifically is preferred that the second reaction stageor subsequent reaction stages if present, is operated under conditionseffective to convert the fluoroolefin contained in the feed stream tothe second reactor stage at a conversion rate that is greater than, andpreferably substantially greater than, the conversion percentage in thefirst reaction stage. In certain preferred embodiments, for example, theconversion percentage in the second reaction stage is from about 20% toabout 99%, depending in large part upon the total number of reactantstages used to affect the overall conversion step. For example, inembodiments consisting of a two-stage reaction system, it iscontemplated that the conversion in the second reaction stage ispreferably greater than 95%, and even more preferably about 100%.However, as those skilled in the art will appreciate from the teachingscontained herein, such a two-stage reaction may not be sufficient toproduce the desired selectivity to the hydrofluorocarbon. In such cases,it is within the scope of the present invention that the conversion stepmay comprise greater than two reaction stages, including in someembodiments as many 10 or more reaction stages.

The size and shape, and other characteristics of the reaction vesselitself may vary widely with the scope of the present invention, and itis contemplated that the vessel associated with each stage may bedifferent than or the same as the vessel associated with the upstreamand downstream reaction stages. Furthermore, it is contemplated that allreaction stages can occur inside a single vessel, provided that meansand mechanisms necessary to control conversion are provided. Forexample, it may be desirable in certain embodiments to utilize a singletubular reactor for each reaction stage, providing conversion control byjudicious selection of the amount and/or distribution of catalystthroughout the tubular reactor. In such a case, it is possible tofurther control the conversion in different sections of the same tubularreactor by controlling the amount of heat removed from or added todifferent sections of the tubular reactor.

The catalyst compositions disclosed in the present invention are usefulin converting fluoroolefins to hydrofluorocarbons. One or more of thehydrogenation catalyst disclosed in the present invention may be usedfor one or more of the reaction stages in accordance with the presentinvention. In certain preferred embodiments, the catalyst preferablycomprises palladium supported on aluminum oxyfluoride.

Thus, certain embodiments of the present methods comprise bringing afluoroolefin and a hydrogenation agent, such as H₂, into contact with afirst amount of catalyst in a first reaction stage to produce a reactionstream comprising hydrofluorocarbon(s), unreacted fluoroolefin andhydrogen; contacting at least a portion of this first effluent streamwith a second amount of catalyst in a second stage of reaction toproduce a hydrofluorocarbon, wherein the second amount of catalyst isgreater than the first amount of catalyst and wherein conversion to thefluoroolefin is higher in the second stage of reaction.

Table 1 sets forth examples of hydrofluorocarbons and fluoroolefins fromwhich they can be obtained (fluoroolefin in left column andcorresponding hydrofluorocarbon in the right column).

TABLE 1 Fluoroolefins Hydrofluorocarbons 1,1,2,3,3,3-hexafluoropropene1,1,1,2,3,3-hexafluoropropane CF₃CF═CF₂ (1216) CF₃CHFCHF₂ (236ea)1,2,3,3,3-pentafluoropropene 1,1,1,2,3-pentafluoropropane CF₃CF═CHF(Z/E-1225ye) CF₃CHFCH₂F (245eb) 1,1,3,3,3-pentafluoropropene1,1,1,3,3-pentafluoropropane CF₃CH═CF₂ (1225zc) CF₃CH₂CHF₂ (245fa)1,3,3,3-tetrafluoropropene 1,1,1,3-tetrafluoropropane CF₃CH═CHF(trans/cis-1234ze) CF₃CH₂CH₂F (254fb) 2,3,3,3-tetrafluoropropene1,1,1,2-tetrafluoropropane CF₃CF═CH₂ (1234yf) CF₃CHFCH₃ (254eb)

EXAMPLE

The following is example of the invention and is not to be construed aslimiting.

Example 1 Hydrogenation of 1,1,1,2,3,3-hexafluoropropene over afluorinated metal oxide and metal fluoride supported Pd catalysts

In example 1, three supported Pd catalysts are compared for conversionefficiency in the hydrogenation of 1,1,1,2,3,3-hexafluoropropene (HFP).More particularly, a 1 wt % Pd/AlO_(x)F_(y), according to the presentinvention was compared to a 1 wt % Pd/AlF₃ and a 1 wt % Pd/MgF₂. 2 g ofcatalyst diluted with 20 ml of Monel packing was charged into a ¾″ Moneltube reactor and was in-situ reduced in 10% H₂/N₂ flow for 2 hours at200° C. HFP was fed into reactor at a rate of 10 g/h, and H₂ was co-fedaccording to a mole ratio of H₂/HFP equal to 1.5. As shown in Table 2,the 1 wt % Pd/AlO_(x)F_(y) catalyst provided an HFP conversion of around98% and a 236ea selectivity of about 99% at 100° C., the 1% Pd/AlF₃catalyst exhibited an HFP conversion of around 80% and a 236easelectivity of about 99.5% at 100° C., and the 1% Pd/MgF₂ one showed anactivity close to 40% and a 236ea selectivity of about 97% at 150° C.,indicating all three catalysts are highly selective to form 236ea.

TABLE 2 HFP hydrogenation over metal fluoride supported Pd catalystsTemp. Conversion, % Selectivity, % Selectivity, % Selectivity, %Catalyst (° C.) HFP 236ea 245eb others 1% Pd/AlO_(x)F_(y)* 100 97.6 98.90.6 0.5 1% Pd/AlF₃ 100 80.4 99.6 0.4 0.0 1% Pd/MgF₂ 150 38.6 97.0 1.51.5 *The AlO_(x)F_(y) support was obtained through the fluorination ofAl₂O₃ in 5.4% HF/N₂ flow for 2 hours at 400° C.

It should be understood that the foregoing description is onlyillustrative of the present invention. Various alternatives andmodifications can be devised by those skilled in the art withoutdeparting from the invention. Accordingly, the present invention isintended to embrace all such alternatives, modifications and variancesthat fall within the scope of the appended claim.

1. An article of manufacture comprising: a. a solid support comprising ametal oxyfluoride or a metal fluoride, wherein said metal fluoride isselected from the group consisting of CrF₃, TiF₄, and ZrF₄; and b. atleast one elemental metal disposed on or within said support, wherein atotal amount of all of the elemental metal(s) disposed on or within saidsupport is less than 1 weight percent, based upon the total weight ofthe elemental metal and support.
 2. The article of claim 1 wherein saidsolid support comprises a metal oxyfluoride and said elemental metal isone or more reduced zero-valent metals.
 3. The article of claim 2wherein said metal oxyfluoride is selected from the group consisting ofmagnesium (II) oxyfluoride, aluminum (III) oxyfluoride, chromium (III)oxyfluoride, titanium (IV) oxyfluoride, and zirconium (IV) oxyfluoride.4. The article of claim 2 wherein said support comprises at least about75 wt. % of said metal oxyfluoride.
 5. The article of claim 2 whereinsaid support consists essentially of said metal oxyfluoride.
 6. Thearticle of claim 2 wherein said elemental metal is selected from thegroup consisting of Pd, Ru, Pt, Rh, Ir, Fe, Co, Ni, Cu, Ag, Re, Os, Au,and any combinations thereof.
 7. The article of claim 1 wherein thetotal amount of the elemental metal comprises about 0.05 to less than 1weight percent of the combined weight of said metal and said support. 8.The article of claim 1 wherein said solid support comprises said metalfluoride and said elemental metal is one or more reduced zero-valentmetals.
 9. The article of claim 8 wherein said support comprises atleast about 75 wt. % of said metal fluoride.
 10. The article of claim 8wherein said support consists essentially of said metal fluoride. 11.The article of claim 8 wherein said elemental metal is selected from thegroup consisting of Pd, Ru, Pt, Rh, Ir, Fe, Co, Ni, Cu, Ag, Re, Os, Au,and any combinations thereof.
 12. The article of claim 8 wherein thetotal amount of the elemental metal comprises about 0.05 to less than 1weight percent of the combined weight of said metal and said support.